Commonly fluids flowing through transmission and distribution lines because of leaks or faults escape from such lines, and the presence and location of such faults or leaks should be quickly and precisely determined in order to reduce the fluid loss.
Various apparatus have been developed for locating a fault in a pressurized pipeline.
Known in the prior art are apparatus based on detection of acoustic oscillations produced in a fault area of the pipeline and propagating at the speed of sound in the fluid products being pumped to the ends of the damaged pipeline.
There is known a fault locating apparatus for a pressurized pipeline, comprising a transducer intended for conversion of mechanical oscillation into an electrical signal, an amplifier, a converter of signals into their ratio, and an indicator, connected in series (cf. USSR Inventor's Certificate No. 603,804 published Apr. 25, 1978).
This apparatus possesses low expedition properties since a considerable time is required to determine the fault location as it is first necessary to define the route of the pipeline being inspected and further to go all over the pipeline route.
The apparatus also does not possess an adequate noise immunity. As a result, it does not allow the fault location to be determined reliably in pipelines laid in regions with a high level of environmental acoustic noise (for example, in the boundaries of a city, in the neighbourhood of reilway crossings, main highway crossings, industrial enterprises, airplane traffic routes). This is explained by the fact that in these regions the environmental noise is often considerably higher than the noise produced by a fault, and the transducer does not distinguish the useful acoustic oscillation from the background one.
The noise immunity of the apparatus can be improved by placing it directly within the pipeline to be inspected.
Known in the prior art is a fault locating apparatus for a pressurized pipeline, comprising a movable pipeline pig having at least two resilient cups isolating one compartment therebetween wherein the electrical and recording portions of the apparatus are carried (cf. U.S. Pat. No. 3,413,653, patented on Nov. 26, 1968).
In order to locate the fault, the apparatus in question is placed inside the pipeline, the recording portion recording output signals of the electrical portion. Then the apparatus is withdrawn from the pipeline, and the records are processed.
However, this apparatus possesses low expedition properties since the data are recorded on a magnetic tape that is to be withdrawn from the pipeline and processed. As a result, a considerable time is required to detect a pipeline fault.
There is also known a fault locating apparatus for a pressurized pipeline, comprising two measuring channels including each a transducer intended for conversion of mechanical oscillation into electrical signals and having an output connected to an amplifier, amplifier outputs being associated with an indicator that is a loop oscillograph (cf. USSR Inventor's Certificate No. 327,425 patented on Jan. 26, 1972).
For the purpose of fault detection, the transducers are installed on the pipeline body at the beginning and at the end of the pressure pipeline portion to be inspected.
The acoustic waves caused by a pipeline fault propagate from the fault area at the speed of sound, the transducers convert these waves into electrical signals recorded on a single oscillogram by the oscillograph loops.
The oscillograms are then visually processed to determine and to measure phase shifts between typical peaks of the acoustic waves and the fault is located by measuring the phase shift between the acoustic waves.
However, the visual processing of the data recorded by the oscillograph lowers the accuracy of the acoustic wave phase shift determination, and, as a result, it brings about a considerable error in fault location.
Furthermore, the apparatus mentioned above has a low speed of operation due to the fact that oscillograms recorded by the oscillograph are processed manually.
Moreover, all of the apparatus discussed hereinabove do not allow to determine large-size breaks and ruptures as well as to keep the pipeline under a constant supervision since the first requires to move along the pipeline to be inspected, the second requires to place the apparatus inside the pipeline and to withdraw it therefrom, while the third requires that the data be manually processed.
Known in the prior art are fault locating apparatus whose principle of operation is based on the detection of the pressure fall wave produced in the fault area and propagating together with the pumped products along the pipeline.
There is known an automatic fault locating apparatus comprising two pick-ups responsive to the pressure drop wave produced in the fault area and propagating together with the pumped product along the pipeline. Pick-up outputs are connected to a time-interval counter (cf. USSR Inventor's Certificate No. 191,284 patented on Jan. 14, 1967).
In order to determine the fault location, the pick-ups are installed on the opposite ends of the pressurized pipeline portion to be checked. The pulse of the pick-up that is nearer to the fault point will reach the time-interval counter earlier than the pulse of the pick-up that is farther from the fault point. The time the fault happens in the pipeline is determined from the response time of the pick-up that is nearer to the damage place, whereas the fault is located by measuring the difference between the pick-up response times.
This apparatus allows to determine large-size faults and ruptures as well as to keep the pressurized pipeline under a constant supervision.
However, this apparatus possesses a low sensitivity and a low noise immunity caused by the susceptibility to service pressure variations.
Known in the prior art is an automatic fault locating apparatus for a pressurized pipeline, comprising pressure pick-ups (cf. USSR Inventor's Certificate No. 478,211 published on July 7, 1975).
An output of each pressure pick-up is connected to a respective amplifier having its output connected to a respective slope and amplitude selector. An output of one of the selectors is connected via a shaper, a communication line and a noise suppressor to one of the inputs of a reading direction indication unit whose other input is connected to another selector. An output of the reading direction indication unit is connected to one of the inputs of a distance-to-fault point indicator whose other input is connected to a setting generator. An output of the distance-to-fault point indicator is connected to an input of a false information reset unit having an output connected to control inputs of the reading direction indication unit and of the distance-to-fault point indicator.
In the event of a pipeline wall rupture the pressure drop wave propagates in both directions from the rupture area and affects alternately on the pressure pick-ups. The reading direction indication unit indicates the sequence in which pick-up pulses come through respective units. When operating, the reading direction indication unit turns on the distance-to-fault point indicator counting the time elapsed between pick-up pulses with the aid of the generator that is a unit time setting device.
This apparatus has a higher sensitivity and noise immunity.
However, this apparatus has a low control accuracy.
There is known an automatic fault locating apparatus for a pressurized pipeline, comprising a receiving unit, a pick-up, an amplifier, a selector, an AND gate, a pulse counter and a pulse generator whose output is connected to an input of the AND gate, all elements being connected in series, and a transmitting unit including a pick-up, an amplifier, a selector, all elements being connected in series and associated through a communication line with the input of the AND gate (cf. USSR Inventor's Certificate No. 589,550 published on Feb. 25, 1978).
The receiving unit further comprises a low-pass filter, a bandpass filter and a shaper, while the transmitting unit further comprises an audio-frequency generator, a bandpass filter and a low-pass filter.
In the event of a pressurized pipeline wall rupture, the pressure drop wave propagates from the rupture area and reaches alternately the receiving unit and the transmitting unit, affecting the pick-ups generating electrical signals fed from the pick-up outputs through the amplifiers to the selectors.
The selected signal of the receiving unit or the communication line signal turns on the AND gate providing the passage of the generator pulses to the pulse counter.
The low-pass filters prevent the passage of this signal to the operating communication equipment, whereas the bandpass filters prevent the passage of working frequencies of the communication equipment to the receiving and transmitting units.
A higher control accuracy is inherent in this apparatus.
However, the necessary use of a special communication line between the receiving unit and the transmitting unit lowers the apparatus reliability due to false signals caused by stray pickups of the communication line, makes the operation of this apparatus more expensive and complicated.